1. Field of the Invention
The present invention relates to an image display apparatus, and particularly, to an image display apparatus such as an HMD (head mounted display) for projecting a two-dimensional image displayed on a liquid crystal display into an observer's pupil through an eyepiece optical system to enable the observer to view an enlarged virtual image of the two-dimensional image.
2. Description of the Prior Art
Conventionally, various types of image display apparatuses have been proposed that project a two-dimensional image displayed on a display unit through an eyepiece optical system to display an enlarged virtual image of the original image. For example, image display apparatuses are known that employ a transmission-type liquid crystal display or a transmission-type screen as a display unit.
In an image display apparatus of the type that employs a transmission-type liquid crystal display, it is so difficult to achieve satisfactorily high density in the transmission-type liquid crystal that it is impossible to achieve a satisfactorily wide angle of view and satisfactorily high-resolution image display. Moreover, an image display apparatus of this type requires a space for accommodating an illumination optical system for illuminating the liquid crystal, and thus it is difficult to make it satisfactorily compact. In contrast, in an image display apparatus of the type that employs a transmission-type screen, it is possible to project a high-resolution image onto the transmission-type screen and thus achieve a satisfactorily wide angle of view and satisfactorily high-resolution image display. However, this image display apparatus, requiring a light source, a projecting optical system, a transmission-type screen, and an eyepiece optical system to be arranged therein, tends to have an unduly long total length, and thus it is even more difficult to make it compact.